In the United States, there are currently as many as 300,000 coronary artery bypass graft (CABG) procedures performed on patients annually. Each of these procedures may include one or more graft vessels which are hand sutured. Until recently, coronary artery bypass procedures have been performed with the patient on cardiopulmonary bypass whereby the heart is stopped with cardioplegia and the surgery is performed on an exposed, stationary heart.
The vast majority of CABG procedures currently performed are accomplished by opening the chest wall to gain access to the coronary vessels. Through the use of heart lung bypass machines and a drug to protect the heart muscle, the heart is stopped and remains still during the procedure. In this setting, the surgeon has ample time and access to the vessels to manipulate hand suturing instruments such as forceps, needle holders and retractors.
However, with increasing costs of hospital stays and increased awareness by patients of other minimally invasive surgical procedures, interest in developing a minimally invasive CABG procedure is increasing. Hospitals need to reduce costs of procedures and patients would like less post-operative pain and speedier recovery times.
In the past, two significant developments in technology played a major role in advancing the whole area of cardiac surgery. The heart-lung machine was invented in the 1950's and underwent significant improvement in design to become a reliable clinical device in the 1960's. The heart-lung machine allows the surgeon to take the heart out of the blood circulation system to work on it in isolation.
The second major development was in myocardial protection. When the heart is isolated from the circulation, it is no longer perfused. After twenty to thirty minutes of ischemia, irreparable damage may occur and no matter how good the repair, the heart function may be inadequate to allow the patient to survive. The development of cardioplegia, a solution which is generally cold and high in potassium, changed everything. This development occurred in the 1970's. Cardioplegia allows very satisfactory protection of the heart so the surgeon can perform an unhurried repair and still expect the heart to work afterward.
An unforeseen consequence of these technology developments was the decline in interest in technology to facilitate and expedite heart surgery. When speed of the surgery was of utmost importance, many developments were proposed to speed surgery. Therefore, while the art in the 1960's and 1970's contained numerous examples of devices intended to expedite heart-related surgery, the incidence of such devices declined after about 1970.
With an increased incentive to reduce costs, there is a renewed interest in expediting cardiothoracic procedures. A few pioneering surgeons are now performing minimally invasive procedures in which the coronary artery bypass is performed through a small incision in the chest wall. There are some surgeons that believe that the best way to perform a minimally invasive coronary artery bypass procedure is to perform the procedure on a beating heart, i.e., without heart-lung bypass and cardioplegia. This minimizes the time it takes to perform the procedure, reduces the cost of the operation by eliminating the heart lung bypass machine and reduces recovery time.
In the case of minimally invasive procedures on a beating heart, the surgeon starts by making a mini-thoracotomy between the fourth and fifth ribs and, sometimes, removing the sternal cartilage between the fourth or fifth rib and the sternum. The space between the fourth and fifth ribs is then spread to gain access to the internal mammary artery (IMA) which is dissected from the wall of the chest. After dissection, it is used as the blood supply graft to the left anterior descending artery of the heart (LAD). The pericardium and the heart are located below the IMA. The pericardium is opened exposing the heart. At this point, the LAD may be dissected from the fissure of the heart and suspended with soft ligatures to isolate the artery from the beating heart. A small arteriotomy is performed in the LAD and the graft IMA is sutured to the LAD.
Heretofore, access to the cardiac vessels is gained for this procedure by sawing the sternum in half and separating the chest wall. Although this procedure is currently well perfected, the patient suffers intense pain and generally requires a long recovery period.
Until recently all bypass graft procedures have been performed by hand suturing tiny vessels together with extremely fine sutures under magnification. The skills and instruments required to sew extremely thin fragile vessel walls together have been perfected over the last twenty years and are well known to the surgical community that performs these procedures.
In the “open chest” surgical setting, the surgeon has adequate access and vision of the surgical site to manipulate the anatomy and instruments. However, in minimally invasive procedures, this access is often severely restricted thereby inhibiting such procedures.
Furthermore, the interest in less invasive surgical approaches is promoting concomitant interest in many areas that were abandoned long ago, including coronary fastening and valve replacement. In view of the above-discussed developments, the inventors have thus identified a need for a device and a method to perform CABG surgery on a beating heart.
Some surgeons are attempting minimally invasive CABG procedures using femoral artery bypass access rather than opening the chest for bypass via the aorta. However, since use of cardioplegia requires additional support and expense during the anastomosis procedure, the inventors believe that it is best to attempt to fasten the anastomosis while the heart is beating. However, this procedure when performed with a hand suturing technique is very imprecise due to the translation of movement from the beating heart to the suspended artery. This may cause imprecise placement of the suture needles. Imprecise placement of the sutures may cause a distortion of the anastomosis which may cause stenosis at the junction.
The sutures used for this procedure are extremely fine (0.001″ in diameter) and are placed less than 1 mm apart. As one can imagine it is difficult enough to place suture needles the size of a small eyelash into a vessel wall with placement accuracy of better than 1 mm; yet to accomplish this feat of precision on a moving target is even more difficult. To make matters worse the site is often obscured by blood because the heart has not been stopped.
Therefore, there is a need for a means and method which permits the forming of a precise anastomosis without requiring the stopping of a beating heart. Still further, there is a need for performing such an anastomosis in a minimally invasive manner.
The current method of hand suturing has the several drawbacks, including the following.
On a beating heart it may be difficult to place the sutures with the position precision required. In a beating heart procedure the surgeon can attempt to minimize the deleterious effects of the movement by using suspension or retraction techniques. However, it is impossible to isolate all movement of the vessel during an anastomosis procedure.
Methods that attempt to stabilize and isolate an artery from the movement of the beating heart may damage the vessel or cause myocardial injury (MI).
In addition to the problem of accurately placing sutures, an incision through the artery wall to open the artery must be made. This, too, is a delicate procedure even on a still heart because the incision must be of a precise length. It is also critical to not penetrate the back wall or side wall of the vessel which will lead to complications. The placement of the initial incision is of paramount importance. The surgeon must pick a suitable location free from calcium deposits, fat and side branches.
Without cardioplegia, blood flow to the heart muscle must also be provided while the heart is beating; therefore, after the initial arteriotomy the surgical field is very bloody and obscured.
Access to the heart vessels other than the LAD will be extremely difficult with minimally invasive hand suturing due to the anatomical location of the posterior wall of the heart.
Although minimally invasive CABG procedures are taking place now with sutured anastomosis they require superlative skills and are therefore not widely practiced.
One of the most vexing problems is that of adequate access. The procedure takes place through an access site created between two ribs. The ribs cannot be spread too far without risk of breaking and the heart lies deep within the chest. The access is through a small, long, dark tunnel. The surgeon must then manipulate tools down this tunnel without obscuring his or her vision.
If special tools are constructed to allow the surgeon to hold suture needles on the end of a long instrument, the added length of the tool only amplifies any inaccurate manipulation. The same is true for any special suturing devices.
If the sutures are not correctly placed in the vessel walls, bunching or leaks may occur. In the minimally invasive procedure this is disastrous usually resulting in the conversion to an open chest procedure to correct the mistake. Any rough handling of the vessel walls is detrimental as inflammation can cause further postoperative complications.
An anastomosis must be leak tight to prevent exsanguination. Therefore, any improvement over sutures must provide a leak free seal in a very confined space, yet should provide proper flow areas in the vessel after healing is complete.
As can be understood from the above discussion, it is necessary to find a way to control the beating heart-induced movement of the vessel while performing the anastomosis in such a way that still allows for exact placement of a fastening means during a beating heart anastomosis procedure.
While the art contains disclosures of several devices that are used to join blood vessels, these devices are primarily directed to an end-to-end anastomosis, and thus are inadequate for CABG procedures. Furthermore, the techniques taught in the prior art often require the vessels to be severely deformed during the procedure. The deformation may be required to fit the vessels together or to fit a vessel to an anchoring device. One cannot just slit the tissue and pull it through a ring to anchor it on a flange. Pulling or stretching the vessel walls produces a very unpleasant and unexpected result. Vessel walls are made of tissue fibers that run in the radial direction in one layer and the longitudinal direction in another layer. In addition, the elasticity of the tissue fibers in the longitudinal direction is greater than those that run radially. Therefore, the tissue will not stretch as easily in the radial or circumferential direction and results in a narrowing or restriction when pulled or stretched in the prior art devices. Vessel walls also have a layer of smooth muscle cells that can spasm if treated harshly. Such manhandling will result in restrictions and stenotic junctions because the vessel walls will react poorly to being treated in such a rough manner and the stretching of the vessel wall will telegraph up the vessel wall due to the high radial stiffness of the vessel structure causing restrictions and spasms in the vessel wall. The prior art fails to teach that the vessels are living tissue and must not be made to conform to rigid fitting-like shapes. Therefore, there is a need for an anastomotic technique that permits handling of blood vessels in a manner that is not likely to cause those blood vessels to react in an undesirable manner
Additionally, the prior art fails to teach methods of ensuring hemostasis so there is no leakage under pressure. It is noted that mechanical devices used to join blood vessels are extremely difficult to seal. Prior art devices are generally directed to accomplishing hemostasis through excessive clamping forces between clamping surfaces or stretching over over-sized fittings.
In order to effect good healing, healthy vessel walls must be brought into intimate approximation. This intimate approximation is now accomplished using sutures. A vascular surgeon is taught how to suture by bringing the vessel edges together with just the right knot tightness. A knot that is too loose may cause the wound to leak and have trouble healing causing excessive scar tissue to form. A knot that is too tight may tear through the delicate tissue at the suture hole causing leaks. The key is to bring the edges together with just the right amount of intimate approximation without excessive compression.
It is further noted that the junctions taught in the prior art are not anatomically correct both for blood flow and for healing. A well made anastomotic junction is not made in a single plane and should accurately follow blood vessel geometry. The junction is more of a saddle shape and the cross section is not necessarily a circle. The junction where the vessel units join is not a constant cross section angle but an angle that varies continuously throughout with respect to any linear reference. In addition, the length of the junction should be many times the width of the opening in order to ensure a low blood flow pressure gradient in the junction and to establish a proper flow area. In fact the best results are obtained if the confluence area is actually oversized. The prior art junctions do not account for such flow characteristics and parameters and are thus deficient. Therefore, there is a need for an anastomotic technique which can establish proper flow characteristics and parameters and that accurately preserves blood vessel geometry, specifically the plural planar nature in which the junction occurs. Furthermore, most anastomoses are made between vessels that are not similar in size. It is therefore necessary to provide a means and method which allow for the accommodation and joining of dissimilarly sized vessels.
In addition, the inventors have found through post surgical follow-up that the supply vessels grow in diameter to accommodate their new role in providing oxygenated blood to the heart; therefore, there is a need to provide an oversized junction to accommodate any increase in the dimension of the graft vessel size. With a rigid ring that has a singular circular cross section of the graft, the fitting does not allow the vessel to provide this increase in flow as the vessels expand to meet the needs of the heart muscle. Still further, the inside lining of the vessel walls (intima) should make contact with each other to have proper healing. The walls of the vessels must come together with just the right amount of approximation to promote good healing. If the incised edges are too far apart scarring will occur causing restrictions. The walls cannot be compressed between two hard surfaces which will damage the vessels. The prior art teaches plumbing-like fittings clamped onto vascular structures. However, clamping and compressing the vessel walls too tightly may cause necrosis of the vessel between the clamps. If necrosis occurs the dead tissue will become weak and most likely cause a failure of the joint. Still further such rings and tubes used to clamp vessels together do not follow the correct anatomical contours to create an unrestricted anastomosis. Failing to account for the way healing of this type of junction occurs and not accounting for the actual situation may cause a poor result. A suture technique has the advantage of having the surgeon making on-the-fly decisions to add an extra suture if needed to stop a leak in the anastomosis. In a mechanical minimally invasive system it will not be possible to put an “extra suture throw” in so the system must provide a way to assure complete hemostasis. Being a mechanical system the approximation will not be 100% perfect. And since the design errs on the side of not over-compressing the tissue there may be very small areas that may present a leak between the edges of the vessel walls. Accordingly healing with prior art techniques using mechanical joining means is not as efficient as it could be. Therefore, there is a need for an anastomotic technique that accounts for the way healing actually occurs and provides proper structural support during the healing process.
When vascular integrity is interrupted, the body quickly reacts to reestablish hemostasis. Circulating blood platelets are quickly mobilized to the injury site and initiate and support the coagulation sequence that leads to the formation of a fibrin plug at the site of injury. Large breaks in vessel walls which are under pressure cannot be effectively sealed by platelets and fibrin without a substrate to collect on. It is critical that the junction of an anastomosis bring two healthy vessel surfaces in close approximation to provide an optimal region for vessel repair and healing, minimizing the distance between healthy endothelial cells on either side of the junction. This allows for the natural control processes which prevent platelet aggregation from extending beyond the area of injury. A more detailed description of the clot limiting process and the healing process can be found in various reference texts, such as “Coagulation: The Essentials”, by Fischbach, David P and Fogdall, Richard P, published by Williams and Wilkins of Baltimore in 1981, the disclosure of Chapter 1 thereof being incorporated herein by reference.
Still further, some vessels are located or sized in a manner that makes placing elements thereon difficult. In such a case, the fewer elements used to perform an anastomosis the better. Therefore, there is a need for a means and a method for performing an anastomosis that can be effected without the need of a hemostatic medium.
Many times, when a CABG operation is undertaken, the patient has multiple clogged arteries. At the present time, the average number of grafts is 3.5 per operation. When multiple grafts are performed, there is sometimes the opportunity to use an existing or newly added supply vessel or conduit for more than one bypass graft. This is known as a jump graft whereby the conduit at the distal end thereof is terminated in a side-to-side anastomosis first, with an additional length of conduit left beyond the first junction. Then, an end of the conduit is terminated in an end-to-end junction. This saves time and resources and may be necessary if only short sections or a limited amount of host graft material is available.
At the present time, existing means and methods of performing an anastomosis do not permit the formation of multiple anastomotic sites on a single graft vessel at both proximal and distal ends. Thus a surgeon will have to use multiple tools to perform multiple anastomoses. This will be either impossible or very expensive.
Therefore, there is a need for a means and a method for performing an anastomosis which will lend itself to efficient and cost-effective multiple by-pass techniques. There is also a need for a means and a method for performing an anastomosis which will lend itself to efficient and cost-effective jump graft techniques.
As discussed above, performing a sutured anastomosis in a minimally invasive manner while the patient's heart is beating requires an extremely high degree of skill and dexterity. Any instrument used in such a procedure must therefore be as easy and efficient to use as possible whereby a surgeon can focus most of his attention on the anastomosis site. The instrument should thus reflect the above-discussed needs as well. Still further, any instrument used in such a procedure must be amenable to efficient manufacture.
The parent applications, incorporated herein by reference and which will be referred to as the parent disclosures, disclose an apparatus and method for forming a precise and anatomically accurate anastomosis on a patient without requiring the patient's heart to be stopped. The means of the parent disclosures includes an instrument that precisely places fasteners on the outside surface of a blood vessel in a position to cause the anastomosis to have the proper flow area and to accurately reflect the geometry of the junction. The means of the parent disclosures further position the inside edges of the two incised blood vessels forming the anastomosis in abutting contact with each other whereby proper healing is promoted.
The present invention amplifies the edge-positioning feature of the parent disclosures so the joint formed is leak free and is anatomically accurate whereby proper healing is promoted. This is still achieved in a minimally invasive surgery situation where proper control of the incised vessels can be difficult to achieve, especially when the patient's heart is beating during the procedure, and does not require a hemostatic medium.
Still further, the accurate and precise control of the vessel walls should be carried out in the most efficient manner in order to most efficiently complete the procedure.
Therefore, there is a need for a means and a method for performing an anastomosis in a minimally invasive manner that fulfills the objectives set forth in the parent disclosures and does so in an efficient manner that forms an accurate and precise joint that is as leak free as possible, even without a hemostatic medium.
As can be understood from the above disclosures, the targets and elements used in performing an anastomosis are often very small. Still further, the procedure will be performed in a very difficult sight area. These two situations combine to make proper alignment of the vessels extremely difficult. However, proper alignment is a necessity.
Therefore, there is a need for a means and a method for properly aligning two vessels during a minimally invasive surgical procedure.
As discussed above and in the parent disclosures, the joint of an anastomosis is formed when the two malleable ring-shaped stents are brought together and attached. An important factor for success for a mechanical anastomotic device is how the tissue is approximated to prevent leaks and to allow the tissue to heal without inflammation or thrombosis, which can lead to a thickening or stenosis at the joint. Thus, the inventors have found that tissue compression at the joint site is important but has not been considered in the prior art. As noted above, it is important not to “over compress” the joint, yet at the same time, the joint must not leak more than a couple of milliliters per minute under physiological blood pressures to allow the natural clotting process to seal any small leaks quickly, after the joint has been formed.
These conflicting considerations present a significant problem. While it might appear to be best to clamp the joint tightly together to prevent leaks, too much force clamping the tissue is not desirable because the tissue healing response is altered by crushing forces. As tissue is crushed or “over compressed”, certain chemical activators are released which can cause blood platelets to aggregate. In addition, injured tissue cells expose a phospholipid surface upon which the clotting cascade coagulation factors interact to form a clot. An otherwise patent anastomosis can be occluded due to an excessive release of clotting factors resulting from a compression injury. There are natural inhibitors to platelet aggregation (prostacyclin) and clot formation, produced when an activated platelet comes in contact with normal vessel wall. Therefore it is important to design a joint that in addition to being virtually leak free, will provide an atraumatic-sealing configuration and present normal tissue and minimal foreign material to the interior of the blood vessel.
The parent disclosures disclose malleable mounting structures having fastening elements thereon for attaching the mounting structures to a vessel. These fastening elements include a body having one end attached to a ring and a tip on the other end. The fasteners are formed by forcing them against arcuate grooves in a manner that is intended to turn the fastener on itself in the manner of a staple. However, the inventors have found that it is important to control the fastener such that when it is engaged with the arcuate groove, it will deform in the desired manner rather than simply fold or crumple.
Therefore, there is a need for a means for controlling the formation of the fastening means disclosed in the parent disclosures to ensure that they will bend in the desired manner.
In the parent disclosures a joint was established using the concepts of fasteners or tines, mounted on a malleable ring-shaped stents. These tines are used to bring the internal layers of the vessel wall to the surface of the malleable ring-shaped stents. In addition, several of the embodiments have employed a hemostatic media externally to promote sealing of any blood at the joint. The inventors have discovered that by staggering the tines on one ring relative to another ring, the tines form the tissue between each other. This interdigitation of the tines reduces leakage to an absolute minimum. An acceptable leak rate is less than 2 ml/min at 200 mm/Hg. However, staggering the tines is not the only factor that contributes to stopping joint leakage, the shape and surface quality of the tines itself also contributes to reducing the leak rate at the joint. The inventors have also discovered the known manufacturing processes produce 90° sharp edges. 90° sharp edges tend to cut through tissue allowing relatively large pathways in which blood leaks through the tine holes. This is mainly due to EDM (electrode discharge machine) or chemical etching methods, which produce a dead sharp edge. Both processes orientate themselves perpendicular to the material that will be machined leaving the sharp edges as a byproduct. Traditional secondary operations used to remove the sharpness from the elements include electropolishing and mechanical deburring. Electropolishing removes extremely small amounts of material from the entire part at the same time. The object to be electropolished is submersed into a chemical bath that is electrically charged thereby uniformly removing small amounts of material on the outer surface of the part. If applied to the malleable stents of interest, it would round the fasteners in an acceptable manner but the tips of the tines would become dull and, unable to pierce the vessel wall and the malleable stent would become too weak from the amount of material which has been removed. Also, the malleable stent would not be perfectly planar due to the inconsistent nature of electropolishing. The deburring process also removes a small amount of material from a part. There are different ways to deburr. One way is a batch process in which many parts are loaded into a rotating container similar to a clothes dryer. A granular abrasive media is added with the parts and the container begins to spin. The media slowly removes any burrs and rounds the edges of the parts. The problem with this process is the parts must be stiff enough to withstand the tumbling effect, and not be bent or deformed by the process. Also parts such as those of interest may tangle with each other when removed making it difficult to separate the parts without damage thereto. Furthermore this type of deburring is not a precision operation. Thus, for the product of interest, some tines may be sharper or thinner than others thereby adversely affecting not only the ability of the joint to be leak-free but also compromising the deployment of the malleable stent on the vessel. Another method of deburring is a manual operation with each malleable stent being individually blasted with a precision instrument. However, the parts may be inconsistent.
Thus, there is a need for a process that can be used to form malleable stents useful in the anastomosis process of interest and which can uniformly remove sharp edges on tines without dulling the tine tip and without removing any material from the malleable body and yet still be cost effective to manufacture in volume production.
Still further, it is often helpful if any artificial elements placed in a patient during a procedure such as the anastomosis of interest in this disclosure be absorbed after the healing process is complete. The anastomotic joint that has been disclosed in parent disclosures has a continuous malleable ring-shaped stent that will remain intact inside the body for the life of the patient while maintaining a predetermined opening. The inventors have observed that sometimes under high demand conditions, graft vessels will grow to make up for an increase in flow demand. While the anastomotic joint is usually created oversized to accommodate this demand it is difficult to predict the exact size that will be needed years ahead. Therefore, there is a need for an anastomosis system that uses elements that can be absorbed by the patient's body after the healing process is complete.